As shown in FIG. 6A, in a conventional voltage step-up type switching power supply IC (Integrated Circuit) 100, the current let flow through an externally fitted inductor Lex is controlled by the switching of a power transistor PT integrated in the IC, and an output voltage Vout to be fed to a load Z is generated by rectifying-smoothing means composed of an externally fitted Schottky-barrier diode SBD and an externally fitted smoothing capacitor Cex.
As conventional arts related to the present invention, various disclosures and proposals have been made, as exemplified by: a semiconductor device capable of preventing parasitic-diode-associated faults that may invite various problems in the circuit built with the semiconductor device (see Patent Publication 1); a rectifier circuit capable of, even in cases where a MOSFET is used as a rectifier device, reducing the voltage fall across the MOSFET and thereby preventing degradation of rectification efficiency (see Patent Publication 2); and a power supply circuit capable of reducing the area occupied by the output-stage circuit thereof and thereby easily preventing a reverse current from flowing from a capacitor that is connected to an output terminal in parallel with a load (see Patent Publication 3).    Patent Publication 1: JP-A-H08-186261 (FIG. 3)    Patent Publication 2: JP-A-H11-233730    Patent Publication 3: JP-A-2003-347913